NAMEI(9) FreeBSD Kernel Developer's Manual NAMEI(9)
NAME
namei, NDINIT, NDINIT_AT, NDFREE_PNBUF - pathname translation and lookup
operations
SYNOPSIS
#include <sys/param.h>
#include <sys/fcntl.h>
#include <sys/namei.h>
int
namei(struct nameidata *ndp);
void
NDINIT(struct nameidata *ndp, enum nameiop op, u_int64_t flags,
enum uio_seg segflg, const char *namep);
void
NDINIT_AT(struct nameidata *ndp, enum nameiop op, u_int64_t flags,
enum uio_seg segflg, const char *namep, int dirfd);
void
NDFREE_PNBUF(struct nameidata *ndp);
DESCRIPTION
The namei facility allows the client to perform pathname translation and
lookup operations. The namei functions will increment the reference
count for the vnode in question. The reference count has to be
decremented after use of the vnode, by using either vrele(9) or vput(9),
depending on whether the LOCKLEAF flag was specified or not.
The NDINIT() macro is used to initialize namei components. It takes the
following arguments:
ndp A pointer to the struct nameidata to initialize.
op The operation which namei() will perform. The following
operations are valid: LOOKUP, CREATE, DELETE, and RENAME. The
latter three are just setup for those effects; just calling
namei() will not result in VOP_RENAME() being called.
flags Operation flags, described in the next section. Several of these
can be effective at the same time.
segflg UIO segment indicator. This indicates if the name of the object
is in userspace (UIO_USERSPACE) or in the kernel address space
(UIO_SYSSPACE).
namep Pointer to the component's pathname buffer (the file or directory
name that will be looked up).
The NDINIT_AT() macro is similar to NDINIT(), but takes one extra
argument:
dirfd File descriptor referencing a directory, or the special value
AT_FDCWD meaning the calling thread's current working directory.
Lookups will be performed relative to this directory.
The NDFREE_PNBUF() macro is used to free the pathname buffer. It must be
called exactly once for each successful namei() call. It takes the
following argument:
ndp A pointer to a struct nameidata that was used in a successful
namei() call.
NAMEI OPERATION FLAGS
The namei() function takes the following set of "operation flags" that
influence its operation:
NC_NOMAKEENTRY An alias for NOCACHE.
NC_KEEPPOSENTRY Keep the positive-caching entry in cache. This flag is
typically combined with NOCACHE to not cache a new
entry, but keep existing one, or with MAKEENTRY.
NOCACHE Avoid namei() creating this entry in the namecache if it
is not already present. Normally, namei() will add
entries to the name cache if they are not already there.
LOCKLEAF Lock vnode on return with LK_EXCLUSIVE unless LOCKSHARED
is also set. VOP_UNLOCK(9) should be used to release
the lock (or vput(9) which is equivalent to calling
VOP_UNLOCK(9) followed by vrele(9), all in one).
LOCKPARENT This flag lets the namei() function return the parent
(directory) vnode, ni_dvp in locked state, unless it is
identical to ni_vp, in which case ni_dvp is not locked
per se (but may be locked due to LOCKLEAF). If a lock
is enforced, it should be released using vput(9) or
VOP_UNLOCK(9) and vrele(9).
WANTPARENT This flag allows the namei() function to return the
parent (directory) vnode in an unlocked state. The
parent vnode must be released separately by using
vrele(9).
FAILIFEXISTS Makes the namei operation fail if the target exists. It
requires that the LOCKPARENT flag is set and LOCKLEAF is
not.
FOLLOW With this flag, namei() will follow the symbolic link if
the last part of the path supplied is a symbolic link
(i.e., it will return a vnode for whatever the link
points at, instead for the link itself).
EMPTYPATH For namei call initialized with NDINIT_AT(), allow the
namep path to be empty. In this case, the dirfd file
descriptor may reference a file of arbitrary type, not
necessary a directory, and lookup returns the vnode for
this file.
LOCKSHARED Lock vnode on return with LK_SHARED, if permitted by the
file system that owns the vnode. The file system must
explicitly permit this by setting MNTK_LOOKUP_SHARED in
mp->mnt_kern_flag during mount and by calling
VN_LOCK_ASHARE() when allocating the vnode. If LOCKLEAF
is specified but shared locking is not permitted, then
the vnode will be returned with LK_EXCLUSIVE.
VOP_UNLOCK(9) should be used to release the lock (or
vput(9) which is equivalent to calling VOP_UNLOCK(9)
followed by vrele(9), all in one).
NOFOLLOW Do not follow symbolic links (pseudo). This flag is not
looked for by the actual code, which looks for FOLLOW.
NOFOLLOW is used to indicate to the source code reader
that symlinks are intentionally not followed.
RBENEATH Requires that namei did not cross the dirfd directory.
The flag is used to implement O_RESOLVE_BENEATH flag for
openat(2).
NAMEILOOKUP The component is embedded in a namei lookup structure,
and the vfs_lookup_nameidata() function can be used to
obtain that structure. This can be useful in
VOP_LOOKUP(9) implementations which need to obtain extra
lookup metadata.
PARAMETERS DESCRIPTORS FLAGS
These flags are used for several purposes. Some of them affects the
global namei operation, some provide information for processing of the
specific path element, for instance, by the VOP_LOOKUP implementation of
the involved filesystem.
RDONLY Specifies that the lookup should act as if the final node
is located on read-only mount. The flag is typically
used by file servers, e.g. NFS, to handle read-only
exports.
ISRESTARTED The namei was restarted with NDRESTART(). This is used
internally for double-root lookups used by ABI
subsystems, after the lookup with native root failed.
The components are reset to the original values, and
lookup is repeated with different root, once.
IGNOREWHITEOUT Ignore whiteouts, e.g. when checking if a directory is
empty.
ISWHITEOUT The result of lookup is whiteout.
DOWHITEOUT Handle whiteouts, the instruction for the VOP_LOOKUP()
filesystem methods.
WILLBEDIR The lookup is done for creating a new entry that will be
directory. It allows the trailing slash in the path
string.
ISOPEN The caller is the code that opens a file. This allows to
weaken the lock mode of the return vnode, if the mount
point indicates extended shared lock support.
NOCROSSMOUNT Do not cross mount points during lookup.
For ".." lookup leading to mount root, returns the root
vnode of the mount instead of the covered vnode of the
filesystem where the mount was placed.
For other lookups passing over mount, do not jump into
the mounted filesystem. This allows to descend into the
file hierarchy otherwise shadowed by the mount point.
NOMACCHECK Do not perform MAC checks during lookup.
AUDITVNODE1 Audit the looked up vnode information, use the first slot
for audit information.
AUDITVNODE2 Same as AUDITVNODE1 but use the second slot.
NOCAPCHECK Do not perform capability checks. If the calling process
is in capability mode, lookup is denied outright.
OPENREAD The lookup was for open and file will be opened for read.
OPENWRITE The lookup was for open and file will be opened for
write.
WANTIOCTLCAPS Leave ioctl caps for the caller. See the description of
namei results.
OPENNAMED Opening a named attribute (directory).
NOEXECCHECK Do not perform check for allowed execution on the
starting directory. It is used to implement the POSIX-
required semantic for openat(2) lookups that must use the
permissions from time the directory was opened, and not
when used for lookup.
MAKEENTRY Looked-up entry is to be added to name cache.
ISSYMLINK Current component is symlink, and it needs the
interpretation according to the FOLLOW or NOFOLLOW flags.
ISLASTCN This is last component of pathname. It is handled
specially, many flags augment its processing.
ISDOTDOT Current component name is "..". Usually implies a need
to specially handle the vnode locking for instantiation
of the target vnode. The generic vn_vget_ino_gen()
function and its more specialized variant vn_vget_ino()
might be useful.
TRAILINGSLASH Path ended in a slash.
CREATENAMED Create a named attribute dir.
ALLOCATED ELEMENTS
The nameidata structure is composed of the following fields:
ni_startdir In the normal case, this is either the current directory
or the root. It is the current directory if the name
passed in does not start with `/' and we have not gone
through any symlinks with an absolute path, and the root
otherwise.
In this case, it is only used by vfs_lookup(), and
should not be considered valid after a call to namei().
ni_dvp Vnode pointer to directory of the object on which lookup
is performed. This is available on successful return if
LOCKPARENT or WANTPARENT is set. It is locked if
LOCKPARENT is set.
ni_vp Vnode pointer to the resulting object, NULL otherwise.
The v_usecount field of this vnode is incremented. If
LOCKLEAF is set, it is also locked.
ni_cnd.cn_pnbuf The pathname buffer contains the location of the file or
directory that will be used by the namei operations. It
is managed by the uma(9) zone allocation interface.
RESULTS
The struct namei member ni_resflags returns the following flags giving
some details of the succesfull operation:
NIRES_ABS The path passed was absolute.
NIRES_STRICTREL Restricted lookup result. Only relative lookups were
done to resolve the path to vnode.
NIRES_EMPTYPATH The EMPTYPATH flag was provided and used. In
particular, the passed path was empty.
If the WANTIOCTLCAPS flag was specified, on return the ni_filecaps member
of the struct namei contains the capabilities of the file descriptor used
as the lookup starting point (dirfd).
RETURN VALUES
If successful, namei() will return 0, otherwise it will return an error.
FILES
src/sys/kern/vfs_lookup.c
EXAMPLES
Assuming the path variable contains a pointer to userspace path string,
the following example looks up the file named by it, and performs
required error and resource handling:
char *path;
struct nameidata nd;
int error;
NDINIT(&nd, LOOKUP, FOLLOW | LOCKLEAF | AUDITVNODE1, UIO_USERSPACE,
path);
if ((error = namei(&nd)) != 0)
return (error);
NDFREE_PNBUF(&nd);
... use nd.ni_vp vnode
ERRORS
Errors which namei() may return:
[ENOTDIR] A component of the specified pathname is not a
directory when a directory is expected.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or
an entire pathname exceeded 1023 characters.
[ENOENT] A component of the specified pathname does not exist,
or the pathname is an empty string.
[EACCES] An attempt is made to access a file in a way forbidden
by its file access permissions.
[ELOOP] Too many symbolic links were encountered in
translating the pathname.
[EISDIR] An attempt is made to open a directory with write mode
specified.
[EINVAL] The last component of the pathname specified for a
DELETE or RENAME operation is `.'.
[EROFS] An attempt is made to modify a file or directory on a
read-only file system.
SEE ALSO
uio(9), uma(9), VFS(9), vnode(9), vput(9), vref(9), vrele(9)
AUTHORS
This manual page was written by Eivind Eklund <eivind@FreeBSD.org> and
later significantly revised by Hiten M. Pandya <hmp@FreeBSD.org>.
BUGS
The LOCKPARENT flag does not always result in the parent vnode being
locked. This results in complications when the LOCKPARENT is used. In
order to solve this for the cases where both LOCKPARENT and LOCKLEAF are
used, it is necessary to resort to recursive locking.
FreeBSD 15.1-STABLE-HBSD September 30, 2025 NAMEI(9)